The present invention relates to a circuit arrangement for operating at least one LED and at least one fluorescent lamp including an input having a first and a second input terminal for connecting an AC supply voltage; a main rectifier having a first and a second input terminal and a first and a second output terminal, wherein the first and the second input terminal of the main rectifier are coupled to the first and the second input terminal for connecting the AC supply voltage, an auxiliary rectifier having a first and a second input terminal and a first and a second output terminal wherein the first and the second input terminal of the auxiliary rectifier are coupled to the first and the second input terminal for connecting the AC supply voltage, an inverter including at least one series circuit formed by a first and a second switch wherein the series circuit is coupled to the first and the second output terminal of the main rectifier, and the output of the inverter having at least one terminal for connecting the fluorescent lamp wherein the first and the second switch each have a control electrode, an operating electrode and a reference electrode, a starting device having a first and a second terminal, wherein its first terminal is coupled to a control electrode of one of the switches of the inverter, a pull-down circuit having a first and a second terminal, wherein its first terminal is coupled to the output of the inverter, and a starting capacitor for providing energy for the starting device.
The invention furthermore relates to a method for operating at least one LED and at least one fluorescent lamp using a circuit arrangement of this type, wherein the second terminal of the starting device and the second terminal of the pull-down circuit are coupled to the first output terminal of the auxiliary rectifier, wherein the starting capacitor is coupled between the first and the second output terminal of the auxiliary rectifier, and wherein there is arranged in parallel with the starting capacitor a series circuit including a first and a second terminal for the least one LED and an LED switch, wherein the LED switch has a control electrode, an operating electrode and a reference electrode, and a timer having a timer capacitor.
FIG. 1 shows a generic circuit arrangement known from the prior art. This circuit arrangement has an input having a first E1 and a second input terminal E2. Via the first E1 and the second input terminal E2, the circuit arrangement can be coupled to a power supply system voltage UN by means of a switch S. The circuit arrangement includes a main rectifier 12 including the diodes D5, D6, D7, D8. The input of the main rectifier 12 is coupled to the input terminals E1, E2. The circuit arrangement furthermore includes an auxiliary rectifier including the diodes D1, D2, D3 and D4. The input of the auxiliary rectifier 14 is likewise coupled to the first E1 and the second input terminal E2. Furthermore, an inverter 16 is provided, which, in the present case, is embodied as a half-bridge circuit and includes a first switch Q1 and a second switch Q2, which are connected in series with one another. This series circuit is coupled to the first A11 and the second output terminal A12 of the main rectifier 12, wherein the voltage provided between the two output terminals A11, A12, which voltage is usually referred to as the intermediate circuit voltage, is backed up by a capacitor C3. The output terminal of the inverter 16 is coupled to a fluorescent lamp LA. The first Q1 and the second switch Q2 each have a control electrode, an operating electrode and a reference electrode. A DIAC D14 is provided as a starting device and one of its terminals is coupled to the control electrode of the switch Q2 of the inverter 16. Moreover, a pull-down circuit 81 is provided, which is formed by the diode D10 in the present case, wherein one of the terminals of the diode D10 is coupled to the output of the inverter 16. Finally, a starting capacitor C1 is provided, which is charged via the nonreactive resistor R1 (first pull-up resistor) and which serves to provide energy for the starting device D14. In the time between the coupling of a power supply system voltage as a result of the closing of the switch S and the starting of the inverter 16 by the DIAC D14, the second pull-up resistor R1 conditions the inverter 16 in such a way that, at the inverter switch whose control electrode is coupled to the starting device, directly before the starting, a voltage greater than zero is present in order to ensure the starting of the inverter 16. Therefore, the resistor is considered to be among the component parts of the inverter 16.
A first LD5 and a second LED LD6 are coupled to the output of the auxiliary rectifier 14 and can be switched on and off by means of a switching transistor Q3. A nonreactive resistor R9 acts as a current limiting resistor.
Proceeding from an off state of this circuit arrangement illustrated in FIG. 1, after the switch S has been switched on once, the LEDs LD5, LD6 are switched on, since the base of the LED switch Q3 is simultaneously brought to a higher potential via the resistor R8 and the LED switch therefore switches on. Timing control is effected via the nonreactive resistor R10 and the capacitor C6 and is referred to hereinafter as LED switch-off delay. In parallel with this, the collector of the transistor Q4 is connected via the nonreactive resistor R1 to the high potential at the output of the main rectifier 12. The base of the transistor Q4 is likewise connected to the high potential at the output of the main rectifier 12 via a timing switching element including the resistors R3 and R4 and also the capacitor C8. The switch-on of the transistor Q4 is delayed by the charge of the capacitor C8. However, the corresponding components are dimensioned such that Q4 becomes conducting before a voltage that would suffice for triggering the DIAC D14 is present at the capacitor C1. The capacitor C1 is likewise coupled to the output A11, A12 of the main rectifier 14 via the nonreactive resistor R1 and is therefore likewise charged. Since the switching transistor Q4 becomes conducting before a voltage sufficient for triggering the DIAC D14 is present at the capacitor C1, the voltage preferably being 33 V or 34 V, the DIAC D14 is not triggered in this situation, for which reason the fluorescent lamp LA remains switched off. Therefore, the combination of the components R3, R4, R5, C8 and Q4 illustrated here is referred to hereinafter as inverter starting preventing device 19. What is important in this case, moreover, is that when the device 19 is active, the starting capacitor is only partly discharged preferably to approximately 20 V. This is achieved by the fact that the impedance from the parallel circuit formed by R3 and R4 divided by the impedance of R1 results approximately in the current gain of the transistor Q4.
If the switch S is then switched off briefly and immediately switched on again, the LEDs LD5, LD6 come on again after the sequence already described. What is crucial, then, is that the capacitor C1 retained a residual voltage during the brief switched-off duration, while the capacitor C8 was discharged via the resistor R4. When the switch S is switched on again, the capacitor C1 therefore has a charge lead over the capacitor C8. This has the effect that the voltage across the capacitor C1 rises to such an extent that the DIAC D14 triggers before the voltage present at the base of the transistor Q4 would suffice to turn on the transistor Q4. As a consequence, the inverter 16 is put into operation, whereby the fluorescent lamp LA is switched on in addition to the LEDs. By means of an LED switch-off device 18, if the inverter 16 is in operation, by means of a fourth winding of the transformer L2 (T) provided therein, the base of the LED switch Q3 is depleted, whereby the LEDs LD5, LD6 are switched off.
The components illustrated in FIG. 1 which have not been mentioned are of secondary importance for understanding the present invention and will therefore not be explicitly introduced. The circuit arrangement illustrated in FIG. 1 basically has two complete energy supplies, a first for the fluorescent lamp and a second, which is branched off in parallel at the AC voltage supply system, with a dedicated full-bridge rectifier including 600 V diodes, and also a series resistor and a switching transistor for the at least one LED. The LED switch is switched to be conductive by means of a pull-up circuit and is switched off by an inversely acting circuit as soon as the inverter oscillates. This requires a series resonant circuit, which is driven in floating fashion by a fourth winding L2 (T) on the half-bridge driving transformer T. The other three windings serve for driving the two switches of the inverter. Preventing the inverter from starting to oscillate is performed by an independent timing circuit, the inverter starting preventing device 19 already mentioned above.
The circuit arrangement from FIG. 1 exhibits a number of disadvantages: thus, the auxiliary rectifier 14 is a rectifier that has to be designed for 600 V if the circuit arrangement is intended to be connected to a customary AC voltage supply system. Since almost the entire output voltage of the auxiliary rectifier 14 is present during operation of the at least one light emitting diode solely at the nonreactive resistor R9, the auxiliary rectifier has to be dimensioned for a large power loss, and thereby considerably reduces the efficiency of the circuit arrangement. The LED switch Q3 has to be able to block up to 600 V in the switched-off state, that is to say when the inverter 16 is active.
A further disadvantage consists in the presence of three timing circuits that are totally independent of one another, namely the LED switch-off delay including R10 and C6, the inverter starting circuit including R1 and C1, and also the inverter starting delay device 19, all three of which together are intended to control an either-or process. The smooth functioning of this system can be achieved exclusively by exact dimensioning of all the components involved, for which reason the overall circuit is extremely susceptible to component and manufacturing tolerances.